Oxide treatment and pressure control for electrodeposition

ABSTRACT

Method and apparatus for electrodepositing a metal onto a substrate. An oxide treatment process is performed on a substrate prior to making electrical contact between a seed layer of the substrate and a conductive contact element which provides a current. In one embodiment, the pressure at the interface between the seed layer and the conductive contact element is controlled to avoid detrimentally affecting a material(s) of the substrate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to methods and apparatus for processing substrates in electrochemical environments.

[0003] 2. Description of the Related Art

[0004] Metallization for sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. In devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio interconnect features with a conductive material, such as copper or aluminum. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) have been used to fill these interconnect features. However, as interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result thereof, plating techniques, such as electrochemical plating (ECP) and electroless plating, for example, have emerged as viable processes for filling sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.

[0005] Metal ECP may be accomplished through a variety of methods using a variety of metals. Copper and copper alloys are generally a choice metal for ECP as a result of copper's high electrical conductivity, high resistance to electromagnetic migration, good thermal conductivity, and it's availability in a relatively pure form. Typically, electrochemically plating copper or other metals and alloys involves initially depositing a thin conductive seed layer over the substrate surface to be plated. The seed layer may be a copper alloy layer having a thickness of about 2000 Å, for example, and may be deposited through PVD or other deposition techniques. The seed layer generally blanket covers the surface of the substrate, as well as any features formed therein. Once the seed layer is formed, a metal layer may be plated onto/over the seed layer through an ECP process. The ECP layer deposition process generally includes application of an electrical bias to the seed layer, while an electrolyte solution is flowed over the surface of the substrate having the seed layer formed thereon. The electrical bias applied to the seed layer attracts metal ions suspended or dissolved in the electrolytic solution to the seed layer. In this manner, ions are plated on the seed layer, thereby forming a metal layer over the seed layer.

[0006] Present designs of cells for electroplating a metal on semiconductor substrates are generally based of a fountain plater type configuration. FIG. 1 is a cross sectional view of a simplified typical fountain plater cell 100 incorporating contact pins. Generally, the fountain plater cell 100 includes an electrolyte container 120 having a top opening, a substrate holder 114 disposed above the electrolyte container 112, an anode 116 disposed at a bottom portion of the electrolyte container 112 and a contact ring 120 contacting the substrate 122. A plurality of grooves 124 are formed in the lower surface of the substrate holder 114. A vacuum pump (not shown) is coupled to the substrate holder 114 and communicates with the grooves 124 to create a vacuum condition capable of securing the substrate 122 to the substrate holder 114 during processing. The contact ring 120 comprises a plurality of metallic or semi-metallic contact pins 126 distributed about the peripheral portion of the substrate 122 to define a central substrate plating surface. The plurality of contact pins 126 extend radially inwardly over a narrow perimeter portion of the substrate 122 and contact a conductive seed layer of the substrate 122 at the tips of the contact pins 126. A power supply (not shown) is attached to the pins 126 thereby providing an electrical bias to the substrate 122. The substrate 122 is positioned above the cylindrical electrolyte container 112 and electrolyte flow impinges perpendicularly on the substrate plating surface during operation of the cell 110.

[0007] While present day electroplating cells and techniques generally achieve acceptable filling of features on larger scale substrate features (i.e., features greater than 1 micron), a number of obstacles impair consistent reliable electroplating onto substrates having sub-micron-sized, high aspect ratio features. One particular obstacle is oxidation accumulating on the seed layer. Prior to immersion into the electrolytic solution of the plating cell, an oxide layer may have formed (inadvertently or intentionally) by exposure to an oxygen-containing environment. Oxidation is known to act as an electrical resistor. As such, the presence of oxidation on the seed layer can reduce the conductivity between the seed layer and the power source (via the contact member). Further, because the oxidation layer may be non-uniform, the resulting plated metal may also be non-uniform. In addition, the oxidation layer may compromise the ability of the subsequently deposited bulk metal to adhere. Therefore, there is a need for a method and apparatus to remove oxide layers from a seed layer prior to making electrical contact therewith.

[0008] Another undesirable effect caused by the presence of an oxide layer is the need for increased relative pressure between the substrate and the cathode contact member. In general, it is desirable to apply a pressure (typically greater than 300 psi) between the substrate plating surface and the cathode contact member sufficient to ensure good, reliable electrical contact therebetween. Insufficient pressure can result in inadequate contact, which may produce non-uniform plating of metal over the seed layer. The presence of an oxide layer requires more pressure than would be needed in the absence of an oxide layer because the oxide layer must be penetrated to allow contact between the underlying seed layer and the cathode contact member. However, excessive pressure can fracture the seed layer and damage other underlying layers. The application of such pressure may be particularly detrimental where one of the underlying layers is a soft and/or porous material, such as a low-k dielectric. The effects of forcibly applying a cathode contact member to a substrate are illustrated in FIG. 2. FIG. 2 shows a side cross sectional view of a substrate 200 comprising a base material 202, a low-k dielectric layer 204, a copper seed layer 206, and an oxide layer 208. As evidenced by FIG. 2, it should be clear that the term “substrate” as used herein refers to a base material which may have one or more layers disposed thereon. The base material 202 may be, for example, Si or SiO. A contact pin 210 is shown disposed on the substrate 200. In particular, the contact pin 210 extends over the oxide layer 208 and has been forced against the substrate 200 with sufficient pressure to penetrate the oxide layer 208. The resulting deformation caused by the contact pin 210 is translated to the low-k layer 204, resulting in a nonuniform profile of the low-k layer 204. In turn, the nonuniform profile of the low-k layer 204 can produce local non-uniformities of the subsequently electroplated layer. In addition,

[0009] Therefore, there is a need for and apparatus and a method for removing oxide from a substrate and uniformly depositing a conductive material on the substrate, where the substrate includes a material capable of being detrimentally affected by pressure necessary to ensure good electrical contact between the substrate and an electrical contact element.

SUMMARY OF THE INVENTION

[0010] Embodiments of the invention generally include applying an oxide removal process to a copper seed layer prior to performing an electrodeposition process.

[0011] One embodiment provides a method of performing electrodeposition on a substrate having an oxide formed on a conductive surface of the substrate. At least a portion of the oxide is removed to define an electrical contact area. The electrical contact area is then contacted with an electrically conductive contact element, wherein the electrically conductive contact element is connected to a power source. A relative pressure is applied between the electrically conductive contact element and the substrate. The relative pressure is less than a critical pressure capable of detrimentally deforming at least one material of the substrate. A material is then electrodeposited on the substrate.

[0012] Another embodiment provides a method of performing an electroplating process on a substrate including a low-k dielectric layer, a seed layer, and an oxide formed on the seed layer. At least a portion of the oxide is removed to expose an electrical contact area of the seed layer. The electrical contact area is then contacted with an electrically conductive contact element, wherein the electrically conductive contact element is connected to a power source. A relative pressure is applied between the electrically conductive contact element and the substrate. The relative pressure is less than a critical pressure capable of detrimentally deforming at least one material of the substrate. A metal is then electroplated on the substrate.

[0013] Yet another embodiment provides an electroplating apparatus having an oxide removal station; an electroplating cell defining electrolyte-containing cavity and including a compliant electrical contact element configured to apply a relative pressure onto a substrate. The relative pressure applied by the compliant electrical contact element is less than a critical pressure capable of detrimentally deforming at least one material of the substrate. A power source is connected to the electrical contact element. The electroplating apparatus further includes at least one robot operable to transport substrates from the oxide removal station to the electroplating cell.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof, which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention, and therefore, are not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0015]FIG. 1 is a side cross sectional view of a prior art electroplating chamber.

[0016]FIG. 2 is a side cross sectional view of a substrate having a contact element disposed thereon and illustrating the deformation of a low-k dielectric layer by the contact element.

[0017]FIG. 3 is a plan view of an electroplating system.

[0018]FIG. 4 is a cross sectional view of an electroplating cell.

[0019]FIG. 4A is a partial cross sectional perspective view of one embodiment of a cathode contact ring and a frontside bladder assembly.

[0020]FIG. 5 is partial cross sectional perspective view of one embodiment of a cathode contact ring having a front side electrically conductive bladder assembly disposed thereon.

[0021]FIG. 6 is partial cross sectional perspective view of one embodiment of a cathode contact ring having a front side electrically conductive bladder assembly disposed thereon and further showing a backside bladder assembly.

[0022]FIG. 7 is a simplified cross sectional view of a substrate wherein the copper oxide layer has been removed to allow contact between a contact element and an exposed copper layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] Embodiments of the invention generally include performing an oxide removal process to remove oxides from a copper seed layer prior to performing an electrodeposition process. The oxide layer on metals is known to inhibit good electrical contact from being made, thereby detrimentally affecting the electrodeposition process. Accordingly, removing the oxide layer to expose the underlying metal improves the electrical contact with a contact element (e.g., the contact pins 419 or the bladder 504). In some embodiments, an oxide removal process is applied to the electrical contact member(s), which supplies current to the seed layer.

[0024] Referring to FIG. 7, a side cross-sectional view of a substrate 700 is shown. The substrate 700 has been processed according to the invention to remove oxide formation from the seed layer. The substrate 700 comprises a base material 702, a low-k dielectric layer 704 and a seed layer 706. The base material 702 may be, for example, Si or SiO. The seed layer 706 may be copper. A contact element 710 is shown disposed on the substrate 700. In particular, the contact element 710 extends over, and in contact with, the oxide layer 708. In contrast to FIG. 2, the low-k layer 704 has not been deformed by application of excess pressure. This is made possible as a result of having removed any oxide to expose the seed layer 706, prior to bringing the substrate into contact with a contact element 710. The absence of an oxide layer on the seed layer 706 allows for good and reliable contact to be made between the contact element 710 and the seed layer 706 with less pressure than would be required had the oxide not been removed.

[0025] In one embodiment, the contact element 710 is a compliant member, such as the bladder 504. As defined herein, “compliant” means sufficiently flexible or compressible to allow the compliant member to deform and follow the contours of the mating surface (i.e., the substrate 700), with the difference in pressure needed for high and low points of the mating surface being a relatively small percentage (for example, between about 10% and about 20%) of the average applied pressure, or pressure applied at a point at an intermediate height. In another embodiment, the contact element is relatively non-compliant (e.g., contact pins 419 described below with reference to FIGS. 4 and 4A), but a pressure control mechanism (e.g., the bladder assembly 430 described below with reference to FIGS. 5 and 6) is provided to avoid application of excessive pressure. Regardless of the particular embodiment, the electrical contact apparatus of the present invention provide a degree of control over the relative pressure between a substrate and electrical contact. Preferably, the pressure at the interface between the substrate and electrical contact (referred to herein as “contact pressure”) is less than a critical pressure, defined herein as a minimum pressure at which one or more of the materials (typically the weakest material) formed on the substrate are detrimentally affected (e.g., cracked). Stated another way, the contact pressure is a pressure which most closely approaches, but does not exceed, the maximum stress or yield strength of the weakest material on the substrate. For example, the critical pressure at which low-k cracks has been measured at between 800 and 3000 psi, depending on the type of low-k. Therefore, in one embodiment for low-k applications, a contact pressure is between about 40 and about 400 psi, and preferably at about 150 psi for the most delicate present-day low k material. In a another embodiment, the contact pressure is less than about 60 psi. In still another embodiment, the contact pressure is less than 30 psi. In still another embodiment, the contact pressure is less than 10 psi.

[0026] Following are a variety of embodiments for removing oxide from a copper seed layer and for providing a current to the copper seed layer in a pressure controlled manner. It should be understood, however, that the following embodiments are merely illustrative, and other embodiments are equally within the scope and spirit of the invention.

[0027] The System

[0028]FIG. 3 is a plan view of an electrochemical deposition system. The electrochemical deposition system 300 generally comprises a loading station 310, a pair of pre-/post-process chambers 311 and 312, a mainframe 314, and an electrolyte replenishing system 320. In one embodiment, the chambers 311 and 312 include any combination of thermal anneal chambers, spin-rinse-dry (SRD) stations and integrated bevel clean (IBC) chambers. For purposes of illustration, embodiment described herein refer to the chamber 311 is a thermal anneal chamber and the chamber 312 is a SRD chamber. Each of the foregoing chambers is available from Applied Materials, Inc. of Santa Clara, Calif. The electrochemical deposition system 300 also includes a control system 322, typically comprising a programmable microprocessor. Preferably, the electrochemical deposition system 300 is enclosed in a clean environment using panels such as Plexiglas panels.

[0029] The mainframe 314 generally comprises a mainframe transfer station 316 and a plurality of processing stations 318. Each processing station 318 includes one or more electrochemical processing cells 340.

[0030] The loading station 310 preferably includes one or more substrate cassette receiving areas 324, one or more loading station transfer robots 328 and at least one substrate orienter 330. A substrate cassette 332 containing substrates 334 is loaded onto the substrate cassette receiving area 324 to introduce substrates 334 into the electrochemical deposition system 300. The SRD station 312 includes one or more SRD modules 336 and one or more substrate pass-through cassettes 338. The substrate pass-through cassette 338 provides access to and from both the loading station transfer robot 328 and a robot 317 in the mainframe transfer station 316.

[0031] An electrolyte replenishing system 320 is positioned adjacent the electrochemical deposition system 300 and connected to the process cells 340 individually to circulate electrolyte used for the electroplating process. Illustratively, the electrolyte replenishing system 320 includes a main electrolyte tank 360, a plurality of source tanks 362, and a plurality of filter tanks 364. The main electrolyte tank 360 is the source of electrolyte for each of the cells 340. The chemical composition of the electrolyte contained in the main electrolyte tank 360 is maintained using chemicals provided from the source tanks 362. The filter tanks 364 are configured to filter the electrolyte in the main electrolyte tank 360 prior to being distributed to the various cells 340.

[0032] In one embodiment, a cleaning process is performed to remove oxide from a surface of a substrate prior to electroplating a conductive material onto the substrate. Preferably, the oxide cleaning process is performed within the system 300 in order to minimize the possibility of reoxidation while transferring the substrates to the process cells 340. Relatedly, the substrate transfer time between the oxide cleaning facility and the process cell 340, in which the electrodeposition is to be performed, is preferably minimized. In one embodiment, one or more of the pre/post process chambers 311 and 312 are configured for performing an oxide cleaning process. In a particular embodiment, the chambers 311,312 are integrated bevel clean chambers, rapid thermal anneal chambers and/or spin-rinse-dry chambers.

[0033] Generally, the process cells 340 are any type of cells adapted for electrodepositing a metal onto a substrate. As such, it is contemplated that the process cells 340 may be, for example, configured for face up or face down electroplating. Further, electrical contact between a substrate and a contact element (e.g., contact element 710) may be made on a front side of a substrate, a backside of a substrate, or both. For brevity, preferred embodiments will be described only with reference to a face down fountain plater cell in which front side electrical contact is made. However, persons skilled in the art will recognize that any other electric deposition techniques/apparatus requiring physical contact between an electrical element and a substrate may be used to advantage.

[0034]FIG. 4 is a partial vertical cross sectional schematic view of an exemplary fountain plater cell 340 for electroplating a metal onto a substrate. The cell 340 is merely illustrative for purposes of describing the present invention. Other cell designs may incorporate and use to advantage the present invention. The electroplating cell 340 generally comprises a container body 402 having an opening on the top portion thereof. The container body 402 is preferably made of an electrically insulative material such as a plastic which does not break down in the presence of plating solutions. The container body 402 is preferably sized and shaped cylindrically in order to accommodate a generally circular substrate at one end thereof. However, other shapes can be used as well. As shown in FIG. 4, an electroplating solution inlet 404 is disposed at the bottom portion of the container body 402. A suitable pump 406 is connected to the inlet 404 to supply/recirculate the electroplating solution (or electrolyte) into the container body 402 during processing. In one aspect, an anode 408 is disposed in the container body 402 to provide a metal source in the electrolyte. The container body 402 includes an egress gap 410 bounded at an upper limit by a shoulder 412 of a cathode contact ring 414 and leading to an annular weir 416. The weir 416 has an upper surface at substantially the same level (or slightly above) a seating surface 417 of a plurality of conducting pins 419 of the cathode contact ring 414. The weir 416 is positioned to ensure that a substrate plating surface 420 of a substrate 421 is in contact with the electrolyte when the electrolyte is flowing out of the electrolyte egress gap 410 and over the weir 416. Alternatively, the upper surface of the weir 416 is positioned slightly lower than the seating surface 417 such that the plating surface 420 is positioned just above the electrolyte when the electrolyte overflows the weir 416, and the electrolyte contacts the substrate plating surface 420 through meniscus properties (i.e., capillary force).

[0035] The cathode contact ring 414 is shown disposed at an upper portion of the container body 402. A power supply 422 is connected to a flange 424 to provide power to the pins 419 which define the diameter of the substrate plating surface 420. The shoulder 412 is sloped so that the upper substrate seating surface of the pins 419 is located below the weir 416 or are at least positionable at a position where the substrate plating surface 420 will be in contact with electrolyte as electrolyte flows over the weir 416. Additionally, the shoulder 412 facilitates centering the substrate 421 relative to the conducting pins 419.

[0036] The contact pins 419 generally comprise a low resistivity, and conversely high conductivity, material resistant to oxidation. In some cases, materials which oxidize to a few monolayers are acceptable, so long as electrons can tunnel through the monolayers. In one embodiment the contact pins 419 comprise a noble metal, e.g., platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh), and/or palladium (Pd). The contact pins 419 may be solid or coated with the desired conductive material. Other conducting materials which may be used (but may be less desirable, due to their susceptibility to oxidation, for example) include copper (Cu), tantalum (Ta), titanium (Ti), molybdenum (Mo), silver (Ag) and gold (Au).

[0037] A mounting plate 432 having an annular flange 434 is seated on an upper rim of the container body 402. The mounting plate 432 (which may be substantially disc-shaped) has a centrally disposed vacuum port 441 formed therein. The vacuum port 441 is preferably attached to a vacuum/pressure pumping system 459 (shown in FIG. 4) adapted to selectively supply a pressure or create a vacuum at a backside of the substrate 421. The pumping system 459 comprises a pump 445, a cross-over valve 447, and a vacuum ejector 449 (commonly known as a Venturi). One vacuum ejector that may be used to advantage in the present invention is available from SMC Pneumatics, Inc., of Indianapolis, Ind. The pump 445 may be a commercially available compressed gas source and is coupled to one end of a hose 451, the other end of the hose 451 being coupled to the vacuum port 441. The hose 451 is split into a pressure line 453 and a vacuum line 455 having the vacuum ejector 449 disposed therein. Fluid flow is controlled by the cross-over valve 447 which selectively switches communication with the pump 445 between the pressure line 453 and the vacuum line 455. Preferably, the cross-over valve has an OFF setting whereby fluid is restricted from flowing in either direction through hose 451. A shut-off valve 461 disposed in hose 451 prevents fluid from flowing from pressure line 455 upstream through the vacuum ejector 449. The desired direction of fluid flow is indicated by arrows.

[0038] As shown in FIG. 4A, an inflatable bladder assembly 430 is disposed on the mounting plate 432 at an upper end of the container body 402 above the cathode contact ring 414. The inflatable bladder assembly 430 comprises a bladder 436 disposed on a lower surface of the mounting plate 432 is thus located opposite and adjacent to the pins 419 with the substrate 421 interposed therebetween. Illustratively, the bladder 436 is partially disposed within an annular recess 440 formed within the mounting plate 432. The bladder 436 is secured by a manifold 446. The manifold 446 comprises a mounting rail 452 disposed between an inner shoulder 448 and an outer shoulder 450. The mounting rail 452 is adapted to be at least partially inserted into an annular mounting channel 443 of the mounting plate 432. A plurality of fluid outlets 454 formed in the manifold 446 provide communication between the bladder 436 and inlets 442 formed in the mounting plate 432. Seals 437, such as O-rings, are disposed in the annular manifold channel 443 in alignment with the inlet 442 and outlet 454 and secured by the mounting plate 432 to ensure an airtight seal. Conventional fasteners (not shown) such as screws may be used to secure the manifold 446 to the mounting plate 432 via cooperating threaded bores (not shown) formed in the manifold 446 and the mounting plate 432.

[0039] In FIG. 4A, lip seals 456 are shown disposed on the inner shoulder 448 and the outer shoulder 450. A portion of the bladder 436 is compressed against the walls of the annular recess 440 by the manifold 446 which has a width slightly less (e.g. a few millimeters) than the annular recess 440. Thus, the manifold 446, the bladder 436, and the annular recess 440 cooperate to form a fluid-tight seal. To prevent fluid loss, the bladder 436 is preferably comprised of some fluid impervious material such as silicon rubber or any comparable elastomer which is chemically inert with respect to the electrolyte and exhibits reliable elasticity. Where needed a compliant covering may be disposed over the bladder 436 and secured by means of an adhesive or thermal bonding. The covering may comprise an elastomer such as Viton™, buna rubber or the like, which may be reinforced by Kevlar™, for example. In one embodiment, the covering and the bladder 436 comprise the same material. The covering has particular application where the bladder 436 is liable to rupturing. Alternatively, the bladder 436 thickness may simply be increased during its manufacturing to reduce the likelihood of puncture.

[0040] The precise number of inlets 442 and outlets 454 may be varied according to the particular application without deviating from the present invention. For example, while FIG. 4 shows two inlets with corresponding outlets, an alternative embodiment could employ a single fluid inlet to the bladder 436.

[0041] A fluid source 438 is fluidly coupled to the bladder 436 via the inlets 442 and the outlets 454. In the illustrative embodiment, quick-disconnect hoses 444 couple the fluid source 438 to the inlets 442. In operation, the fluid source 438 supplies a fluid, i.e., a gas or liquid, to the bladder 436 allowing the bladder 436 to be inflated to varying degrees.

[0042] Persons skilled in the art will readily appreciate other arrangements which do not depart from the spirit and scope of the present invention. For example, where the fluid source 438 is a gas supply it may be coupled to hose 451 thereby eliminating the need for a separate compressed gas supply, i.e., pump 445. Further, a separate gas supply and vacuum pump may supply the backside pressure and vacuum conditions. While it is preferable to allow for both a backside pressure as well as a backside vacuum, a simplified embodiment may comprise a pump capable of supplying only a backside vacuum. However, as will be explained below, deposition uniformity may be improved where a backside pressure is provided during processing. Therefore, an arrangement such as the one described above including a vacuum ejector and a cross-over valve is preferred.

[0043] Those skilled in the art will readily recognize other embodiments which are contemplated by the present invention. For example, while FIG. 4A shows a preferred bladder 436 having a surface area sufficient to cover a relatively small perimeter portion of the substrate backside at a diameter substantially equal to the contact pins 419, the bladder assembly 430 may be geometrically varied. Thus, the bladder assembly 430 may be constructed using more fluid impervious material to cover an increased surface area of the substrate 421.

[0044] The operation of the bladder assembly 430 will be described in detail below.

[0045] In another embodiment, the contact element which provides electrical current to a seed layer from a power source is a compliant element, adapted to mitigate the possibility of the forming soft/fragile underlayers formed on a substrate. In one embodiment, the compliant element is an inflatable electrically conductive contact element. FIGS. 5 and 5A show a cross-sectional view of one embodiment of an inflatable electrically conductive contact element assembly 500. For brevity and simplicity, identical components previously described will be referenced by like numerals.

[0046] The electrically conductive bladder assembly 500 is shown disposed on an annular contact ring 502. The electrically conductive bladder assembly 500 comprises a electrically conductive bladder 504. In one embodiment, the electrically conductive bladder 504 is a continuous annular ring. In one aspect, the use of a continuous ring provides a continuous current conductivity interface about a periphery of a substrate 421. However, in another embodiment, the electrically conductive bladder 504 may comprise a plurality of discrete inflatable contact elements. In any case, the bladder 504 is preferably disposed in an exclusion area of the substrate 421 to avoid rendering an unacceptably large portion of the substrate seed layer unusable. In one embodiment, the exclusion area of a 200 mm substrate is between about 1 mm and about 3 mm wide.

[0047] The electrically conductive bladder 504 is disposed in an annular recess 506 formed in the annular contact ring 504. One or more inlets 508 are formed in the contact ring 504 and lead into a relatively enlarged annular mounting channel 510. The electrically conductive bladder 504 is secured within the annular recess 506 by a retaining member 514. The retaining member 514, in turn, may be secured to the annular contact ring my fasteners, such as screws (not shown). Illustratively, a plurality of O-rings 507 (one shown) may be disposed in the mounting channel 510 between each inlet 508 and the retaining member 514. At least one outlet 512 is formed in the retaining member 514 in order to fluidly couple the inlets 508 with the electrically conductive bladder 504. Each inlet 508 is fluidly coupled to a fluid channel 516 formed in the contact ring 504. The fluid channel 516, in turn, is fluidly coupled to a fluid source 518 via a fluid supply line 520. Accordingly, the fluid source 518 is coupled to the bladder 504 via the fluid channel(s) 516, inlet(s) 508 and outlet(s) 512 to supply a fluid, i.e., a gas or liquid, to the bladder 504 allowing the bladder 504 to be inflated to varying degrees. In this manner, the relative pressure between the bladder 504 and a substrate 421 can be controlled by inflating the bladder 504.

[0048] To prevent fluid loss, the bladder 504 is preferably comprised of some fluid impervious material such as silicon rubber or any comparable elastomer which is chemically inert with respect to the electrolyte and exhibits reliable elasticity. In one embodiment, a compliant covering may be disposed over the bladder 504 and secured by means of an adhesive or thermal bonding. The covering may comprise an elastomer such as Viton™, buna rubber or the like, which may be reinforced by Kevlar™, for example. In one embodiment, the covering and the bladder 504 comprise the same material. The covering has particular application where the bladder 504 is liable to rupturing. Alternatively, the bladder 504 thickness may simply be increased during its manufacturing to reduce the likelihood of puncture.

[0049] In any case, the bladder 504 is electrically conductive and is connected to a power supply 422 capable of providing a current to the bladder 504. In one embodiment, the bladder 504 is made electrically conductive by disposing a conductive covering over the bladder 504. For example, a metal strip may be wrapped around the outer surface of the bladder 504. In another embodiment, electrically conductive material may be embedded within the bladder 504, thereby “metallizing” the bladder 504.

[0050] The conductive portion of the bladder 504 preferably comprises a low resistivity, high conductivity, material resistant to oxidation. For example, in one embodiment the bladder 504 comprises a noble metal, e.g., platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh), and/or palladium (Pd). Other conducting materials which may be used include copper (Cu), tantalum (Ta), titanium (Ti), molybdenum (Mo), beryllium (Be), silver (Ag) and gold (Au). In some embodiments, the bladder 504 may be solid or coated with the desired conductive material. Persons skilled in the art will recognize other embodiments.

[0051] In another embodiment, the front side electrically conductive bladder 504 is used in combination with the backside bladder assembly 430 described above with reference to FIG. 4. One such embodiment shown in FIG. 6. The provision of a bladder on either side of a substrate allows for additional pressure control. Further, the bladder 436 disposed on the backside of a substrate may mitigate generation of particulate (i.e., by relative friction between the mounting plate 432 and the substrate 420).

[0052] It should be understood that the metallized bladder 504 is merely one embodiment providing a compliant contact element. Persons skilled in the art will recognize a variety of other compliant contact elements suitable for electrodeposition processes. For example, the contact pins 419 shown in FIG. 4 may be made compliant. In one embodiment, the contact pins 419 are manufactured to be flexible members, much like a leaf spring. In this way, the radially extended contact pins 419 may be deflected from a plane in which the pins reside in the absence of an applied force. The degree of deflection may be controlled according to the amount of applied pressure and the flexibility of the pins.

[0053] The operation of the bladder assembly 500 will be described below.

[0054] System Operation: Oxide Cleaning Processes and Pressure Control

[0055] The present invention contemplates a variety of oxide cleaning and/or treatment techniques. In one embodiment, substrates are remotely cleaned (remove oxides formed on a seed layer of the substrates) and then transferred to the system 300. The substrates may be introduced to the loading station 310 and then transferred to one of the various process cells 340 by operation of the robots of the system 300. In another embodiment, the oxide cleaning process is performed within the system 300. That is, substrates are transferred to an integrated cleaning station (described above) and subsequently to one of the various process cells 340. In yet another embodiment, the process cells 340 are adapted to perform in situ cleaning. The latter embodiment minimizes the possibility of reoxidation during substrate transfer because the cleaning and electrodeposition are performed in the same chamber.

[0056] In general, the oxide cleaning process performed prior to electrodeposition may be any of a variety of processes, including known and unknown processes. One method of removing oxide is by the application of an acid to dissolve oxides formed on a seed layer. Illustrative acids which may used to dissolve oxides are shown in Table I. TABLE I Chemical Composition Concentration(s) Sulfuric acid in deionized 0.1 to 6% by wt water (DI) HF in DI 0.1 to 6% by wt HCl in DI 0.1 to 6% by wt HCl and NH₄OH in DI 0.1 to 6% by wt for HCl, and 0.1 to 2% for NH₄OH HOCH₂COOH (Glycolic 1 to 30% by wt acid) in DI

[0057] In one aspect, acids may allow selective removal the oxide from the seed layer to avoid undesirably diminishing the available seed material. Other techniques capable of achieving selectivity between the oxide and the underlying metal may also be used to advantage.

[0058] In another embodiment, a reducing agent is used to reduce the oxide. That is, the oxide is exposed to hydrogen, thereby allowing the oxygen in the oxide to combine with the hydrogen, resulting in water. The water evaporates or can be boiled away to leave the exposed metal seed layer. In one embodiment, the reducing agent may be an acid which provides a source of hydrogen atoms or hydrogen ions. Illustrative reducing agents and their respective concentrations are provided below in Table II. The advantage of using the reduction process is that the oxide layer that forms over the seed layer reacts with a portion of the seed layer, and therefore, assuming that a copper seed layer is implemented, for example, then the oxide layer includes some copper from the seed layer therein. This copper generally forms a copper oxide layer. As such, when the copper oxide layer is removed, a portion of the seed layer is also removed in conventional oxide removal processes. However, when the reduction process of the invention is implemented, the chemical reaction utilized is configured to remove the oxygen component of the oxide, while leaving the cupper component of the oxide layer. As such, the copper content or thickness of the seed layer is generally unchanged or unaltered TABLE II Chemical Composition Concentration(s) UV activated H2 gas 3 to 100% H2 in Ar or other relatively inert gas, such as N2 Plasma activated H2 gas 3 to 100% H2 in Ar or other relatively inert gas, such as N2 Carboxyl Acid 1 to 30% by weight Formic Acid 1 to 30% by weight Aldehydes (e.g., acetaldehyde 10 to 100% by weight or propionaldehyde) Alcohols (e.g., methanol, 10 to 100% by weight ethanol)

[0059] In one embodiment, hydrogen ions in a liquid acid react with cupric oxide on the surface of the seed layer to reduce the copper oxide back to copper, while creating H₂O as part of the reaction. Copper reacting in this manner is dissolved into the acid, since there is a charge transfer. The reaction is described by the following equation:

CuO+2H⁺⇄Cu²⁺(aq)+H₂O  (Equation 1)

[0060] Embodiments further provide for the application of an acid followed by a degassed deionized water rinse. Use of a deionized rinse flushes the dissolved oxygen from the substrate surface, thereby reducing the possibility for re-oxidation of the metal layer prior to making contact. In one embodiment, an oxidation removal step and a deionized rinse are performed in a spin-rinse-dry chamber (e.g., one of chambers 311 and 312 of FIG. 3).

[0061] In another embodiment, oxidation removal is performed in the presence of a plasma. For example, a hydrogen plasma may be generated and allowed to interact with the oxidized surface of a substrate having a copper seed layer. The resulting reaction is described by the following equation:

CuO+2H⁺+2e⁻⇄Cu(s)+H₂O  (Equation 2)

[0062] Note that according to this reaction oxidized copper (CuO) reacts with hydrogen ions to produce solid copper. In one aspect, an advantage achieved by plasma cleaning in this manner is minimizing the amount of copper removed from the substrate, including the copper that was initially in oxidized state. This result is particularly advantageous for thin seed layers since last of the seed copper is removed. In a particular embodiment the hydrogen plasma process is performed in an anneal chamber. Accordingly, it is contemplated that an anneal chamber, e.g., chamber 311 or 312, is equipped with a plasma source capable of generating a plasma from a hydrogen-containing gas, such as forming gas. In one embodiment, the hydrogen containing gas is about 96% nitrogen and about 4% hydrogen.

[0063] When performing oxide removal processes it may be desirable to remove only that portion of the oxide necessary to make electrical contact with a contact element (e.g., the bladder 504). As such, in the case of using an acid as a reducing agent or dissolving agent, application of the acid may be restricted to electrical contact area on a substrate (typically on a perimeter of the substrate). To this end, acid may be applied by a brush or swab. In one embodiment, the acid applicator is located in an integrated bevel clean (IBC) chamber a spin-rinse-dry (SRD) chamber, such as one of the chambers 311, 312 described above with reference to FIG. 3. Illustratively, applicators 313 (two shown) are shown disposed in the pre/post processing chamber 312. The applicators 313 may be pivot mounted or fixed in place and may comprise a brush, nozzle or other fluid applicator disposed at one end. Preferably, the applicators 313 are configured to apply a fluid with minimal splashing, in order to avoid affecting areas of a substrate which do not require treatment and to conserve the fluid being applied. A fluid feed (not shown) may be coupled to the applicators 313 to replenish oxide treatment fluid as needed.

[0064] In one embodiment, the oxide cleaning techniques described herein can be applied to the electrical contact element, e.g., the contact pins 419 and the electrically conductive bladder 504. Using this approach would allow less expensive materials to be used for the electrical contact element (i.e., materials relatively less resistant to oxidation). In one embodiment, the contact elements are cleaned using electrolyte fluid in the container body 402 (FIG. 4), which may have the appropriate oxide treatment chemistry as described herein.

[0065] Following the oxide removal process (on the substrate and, in some embodiments, on the electrical contact element), the substrate may be brought into contact with the contact element in order to supply a current to the exposed seed layer. Where the contact assembly of FIG. 4 is used, a substrate 421 is introduced into the container body 402 by securing it to the lower side of the mounting plate 432. This is accomplished by engaging the pumping system 459 to evacuate the space between the substrate 421 and the mounting plate 432 via port 441 thereby creating a vacuum condition. The bladder 436 is then inflated by supplying a fluid such as air or water from the fluid source 438 to the inlets 442. The fluid is delivered into the bladder 436 via the manifold outlets 454, thereby pressing the substrate 421 uniformly against the contact pins 419. An electrolyte is then pumped into the cell 340 by the pump 406 and flows upwardly inside the container body 402 toward the substrate 421 to contact the exposed substrate plating surface 420. The power supply 422 provides a negative bias to the substrate plating surface 420 via the contact pins. As the electrolyte is flowed across the substrate plating surface 420, ions in the electrolytic solution are attracted to the surface 420. The ions then deposit on the surface 420 to form the desired film.

[0066] Because of its flexibility, the bladder 436 deforms to accommodate the asperities of the substrate backside and contact pins 419 thereby mitigating misalignment with the conducting pins 419. The compliant bladder 436 prevents the electrolyte from contaminating the backside of the substrate 421 by establishing a fluid tight seal at a perimeter portion of a backside of the substrate 421. Once inflated, a uniform pressure is delivered downward toward the pins 419 to achieve substantially equal force at all points where the substrate 421 and pins 419 interface. The force can be varied as a function of the pressure supplied by the fluid source 438. Further, the effectiveness of the bladder assembly 430 is not dependent on the configuration of the cathode contact ring 414. For example, while FIG. 4 shows a pin configuration having a plurality of discrete contact points (i.e., the surfaces 417 of the pins 419), the cathode contact ring 414 may also be a continuous surface.

[0067] Additionally, the fluid tight seal provided by the inflated bladder 436 allows the pump 445 to maintain a backside vacuum or pressure either selectively or continuously, before, during, and after processing. Generally, however, the pump 445 is run to maintain a vacuum only during the transfer of substrates to and from the electroplating cell 340 because it has been found that the bladder 436 is capable of maintaining the backside vacuum condition during processing without continuous pumping. Thus, while inflating the bladder 436, as described above, the backside vacuum condition is simultaneously relieved by disengaging the pumping system 459, e.g., by selecting an OFF position on the cross-over valve 447. Disengaging the pumping system 459 may be abrupt or comprise a gradual process whereby the vacuum condition is ramped down. Ramping allows for a controlled exchange between the inflating bladder 436 and the simultaneously decreasing backside vacuum condition. This exchange may be controlled manually or by computer.

[0068] The operation using the bladder assembly 500 according to the embodiments of FIG. 5 or FIG. 5 may be similarly performed. Accordingly, a detailed description of the operation is not necessary. Briefly, the conductive side of the substrate 421 (i.e., the surface having the seed layer disposed thereon) is disposed on the bladder 504. The fluid source 518 is activated to inflate the bladder 504 to a desired degree. In the embodiment of FIG. 6, the bladder 436 may be similarly inflated by the fluid source 438. Operation of the power supply 422 establishes a potential drop between the anode 408 and the electrically conductive bladder 504 to initiate electroplating of a metal onto the substrate 421.

[0069] In one aspect, the oxide removal processes provided herein reduce the electrical contact resistance between the contact element and the seed layer. Accordingly, good, reliable electrical contact between the contact element and the seed layer may be achieved with relatively less pressure, as compared to techniques in which oxide removal is not performed. As a consequence, the integrity of the underlying low-k layer is protected and the possibility of cracking of the seed layer is lessened or eliminated. Further, the compliant electrical contacts (e.g., the bladder assemblies) provided herein provide a convenient apparatus and method for controlling the relative pressure between a substrate and an electrical contact element. When oxide removal techniques are combined with pressure control techniques, uniform plating results can be achieved.

EXAMPLE

[0070]FIG. 8 shows the results of resistance contact measurements with respect to pressure for two contact elements, Pin A and Pin B. The units on both the horizontal and vertical axes are arbitrary. The contact resistance was measured for each pin without an oxide treatment process and with an oxide treatment process. The substrates used had seed layers 400 Angstroms thick and were treated with an oxide cleaning liquid comprising 1% H₂SO₄ by weight, in DI water. The process time was about 10 seconds of application with the 1% acid, followed by a DI rinse. The substrates were then exposed to air for 20 minutes before the contact resistance measurement was made.

[0071] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

What is claimed is:
 1. A method of performing electrodeposition, comprising: providing a substrate having an oxide layer on a conductive surface thereof; performing an oxide reduction process on the oxide layer to define an electrical contact area; contacting the electrical contact area with an electrically conductive contact element, wherein the electrically conductive contact element is connected to a power source; applying a relative pressure between the electrically conductive contact element and the substrate less than a critical pressure capable of detrimentally deforming at least one material of the substrate; and electrodepositing a material on the substrate.
 2. The method of claim 1, wherein the at least one material is a low-k dielectric.
 3. The method of claim 1, wherein the relative pressure is less than about 60 psi.
 4. The method of claim 1, wherein the relative pressure is between about 10 psi and about 60 psi.
 5. The method of claim 1, wherein the relative pressure is between about 10 psi and about 30 psi.
 6. The method of claim 1, wherein the electrical contact area is an exposed portion of a seed layer.
 7. The method of claim 1, wherein performing the oxide reduction process comprises removing at least a portion of the oxide and leaving the conductive layer thereunder generally unaltered.
 8. The method of claim 1, wherein performing the oxide reduction process comprises applying an acid to the substrate, wherein the acid is configured to react with the oxide layer to remove oxygen and leave the conductive layer unaltered.
 9. The method of claim 1, wherein performing the oxide treatment process comprises chemically reducing at least a portion of the oxide into a metal.
 10. The method of claim 1, wherein performing the oxide treatment process comprises dissolving the oxide.
 11. The method of claim 1, wherein performing the oxide treatment process comprises exposing the portion of the oxide to a plasma.
 12. The method of claim 1, wherein applying the relative pressure comprises inflating a bladder in contact with the substrate.
 13. The method of claim 1, wherein the electrically conductive contact element is an inflatable bladder and wherein applying the relative pressure comprises inflating the bladder.
 14. The method of claim 1, further comprising performing an oxide treatment process on the electrically conductive contact element prior to contacting the electrical contact area with the electrically conductive contact element.
 15. A method of performing an electroplating process, comprising: providing a substrate comprising a low-k dielectric layer, a seed layer, and an oxide formed on the seed layer; performing an oxide treatment process on at least a portion of the oxide to expose an electrical contact area of the seed layer; contacting the electrical contact area with an electrically conductive contact element, wherein the electrically conductive contact element is connected to a power source; applying a relative pressure between the electrically conductive contact element and the substrate less than a critical pressure capable of detrimentally deforming at least one material of the substrate; and electroplating a metal on the substrate.
 16. The method of claim 15, wherein the oxide treatment process is performed in one of a spin-rinse-dry chamber and an integrated bevel clean chamber.
 17. The method of claim 15, wherein the relative pressure is less than about 60 psi.
 18. The method of claim 15, wherein the relative pressure is between about 10 psi and about 60 psi.
 19. The method of claim 15, wherein the relative pressure is between about 10 psi and about 30 psi.
 20. The method of claim 15, wherein performing the oxide treatment process comprises applying an acid to the substrate.
 21. The method of claim 15, wherein performing the oxide treatment process comprises chemically reducing the oxide into a metal.
 22. The method of claim 15, wherein performing the oxide treatment process comprises dissolving the oxide.
 23. The method of claim 15, wherein performing the oxide treatment process comprises exposing the portion of the oxide to a plasma.
 24. The method of claim 15, wherein applying the relative pressure comprises inflating a bladder in contact with the substrate.
 25. The method of claim 15, wherein the electrically conductive contact element is an inflatable bladder and wherein applying the relative pressure comprises inflating the bladder.
 26. The method of claim 25, wherein the relative pressure is less than about 60 psi.
 27. The method of claim 25, wherein the relative pressure is between about 10 psi and about 60 psi.
 28. The method of claim 25, wherein the relative pressure is between about 10 psi and about 30 psi.
 29. An electroplating apparatus, comprising: an oxide removal station; an electroplating cell defining electrolyte-containing cavity and comprising a compliant electrical contact element configured to apply a relative pressure onto a substrate less than a critical pressure capable of detrimentally deforming at least one material of the substrate; a power source connected to the electrical contact element; and at least one robot operable to transport substrates from the oxide removal station to the electroplating cell.
 30. The apparatus of claim 29, wherein the oxide treatment station comprises an acid applicator configured to apply an acid to at least a portion of the substrate.
 31. The apparatus of claim 29, wherein the oxide treatment station comprises a plasma source.
 32. The apparatus of claim 29, wherein the oxide treatment station comprises an integrated bevel clean chamber.
 33. The apparatus of claim 32, wherein the integrated bevel clean chamber comprises an acid applicator configured to apply an acid to at least a portion of the substrate.
 34. The apparatus of claim 29, wherein the oxide treatment station comprises a spin-rinse-dry chamber.
 35. The apparatus of claim 34, wherein the spin-rinse-dry chamber comprises an acid applicator configured to apply an acid to at least a portion of the substrate. 